1. Field of the Invention
The present invention relates to an electronically controlled fuel-supply system for internal combustion engines, and specifically to a system accommodating a pressure regulator in a fuel tank, which regulator is provided for properly regulating a fuel pressure of fuel delivered to each fuel-injection valve assembly.
2. Description of the Prior Art
As is generally known, in conventional electronically-controlled fuel-injection systems, a fuel pressure of fuel delivered to an electromagnetically-operated fuel-injection valve assembly is regulated by a pressure regulator, so that a fuel-injection amount per unit hour with respect to the respective fuel-injection valve assembly is held essentially constant. In general, a fuel-supply amount (a fuel-injection amount) delivered to the engine cylinder would be adjusted by varying a pulse-width (a controlled valve-opening time interval) of a fuel-injection pulse signal output to each fuel-injection valve assembly. The pressure regulator is generally provided in the vicinity of the associated fuel-injection valve assembly of the engine, to properly adjust an amount of fuel returning from the fuel-injection valve assembly via a fuel return passage into a fuel tank, and consequently to maintain the pressure difference between a fuel pressure of fuel to be injected from the fuel-injection nozzle of the fuel-injection valve assembly and a pressure (corresponding to an intake manifold pressure or a boost pressure) acting onto the open end of the nozzle valve of the fuel-injection nozzle at a predetermined constant value. In the case that the pressure regulator is provided in the vicinity of the engine cylinder block or the engine cylinder head, fuel which is returned into the fuel tank through a fuel-return passage for the purpose of fuel-pressure regulation, tends to absorb heat produced by the engine, and as a result temperatures in the fuel tank necessarily tend to rise undesirably. Additionally, the conventional system requires a very long fuel-return passage intercommunicating the pressure regulator and the fuel tank. To avoid this, there has proposed and developed a fuel-supply system equipped with a pressure regulator accommodated in a fuel tank. In such a system, fuel returned from the pressure regulator via the return passage to the fuel tank cannot be influenced by heat produced by the engine, and thus a temperature-rise in the fuel tank may be suppressed to a minimum. However, in the same manner as the former system employing a pressure regulator in the vicinity of the engine, in case of the latter system employing a pressure regulator in a fuel tank, an intake manifold pressure (a boost pressure) acting onto the open end of the nozzle valve of the fuel-injection nozzle, which pressure serves as a reference pilot pressure for the regulator, must be introduced into the inlet port of the regulator for the purpose of regulating-action of the fuel pressure toward a desired pressure level. As can be appreciated, the latter system suffers from the drawback that a length of a boost-pressure conduit required for extracting or introducing the boost pressure in the intake manifold to the inlet of the pressure regulator accommodated in the fuel tank is extremely long.